Myeloid-derived suppressor cells attenuate the antitumor efficacy of radiopharmaceutical therapy using 90Y-NM600 in combination with androgen deprivation therapy in murine prostate tumors

RATIONALE

Androgen deprivation therapy (ADT) is pivotal in treating recurrent prostate cancer and is often combined with external beam radiation therapy (EBRT) for localized disease. However, for metastatic castration-resistant prostate cancer, EBRT is typically only used in the palliative setting, because of the inability to radiate all sites of disease. Systemic radiation treatments that preferentially irradiate cancer cells, known as radiopharmaceutical therapy or targeted radionuclide therapy (TRT), have demonstrable benefits for treating metastatic prostate cancer. Here, we explored the use of a novel TRT, 90Y-NM600, specifically in combination with ADT, in murine prostate tumor models.

METHODS

6-week-old male FVB mice were implanted subcutaneously with Myc-CaP tumor cells and given a single intravenous injection of 90Y-NM600, in combination with ADT (degarelix). The combination and sequence of administration were evaluated for effect on tumor growth and infiltrating immune populations were analyzed by flow cytometry. Sera were assessed to determine treatment effects on cytokine profiles.

RESULTS

ADT delivered prior to TRT (ADT→TRT) resulted in significantly greater antitumor response and overall survival than if delivered after TRT (TRT→ADT). Studies conducted in immunodeficient NRG mice failed to show a difference in treatment sequence, suggesting an immunological mechanism. Myeloid-derived suppressor cells (MDSCs) significantly accumulated in tumors following TRT→ADT treatment and retained immune suppressive function. However, CD4+ and CD8+ T cells with an activated and memory phenotype were more prevalent in the ADT→TRT group. Depletion of Gr1+MDSCs led to greater antitumor response following either treatment sequence. Chemotaxis assays suggested that tumor cells secreted chemokines that recruited MDSCs, notably CXCL1 and CXCL2. The use of a selective CXCR2 antagonist, reparixin, further improved antitumor responses and overall survival when used in tumor-bearing mice treated with TRT→ADT.

CONCLUSION

The combination of ADT and TRT improved antitumor responses in murine models of prostate cancer, however, this was dependent on the order of administration. This was found to be associated with one treatment sequence leading to an increase in infiltrating MDSCs. Combining treatment with a CXCR2 antagonist improved the antitumor effect of this combination, suggesting a possible approach for treating advanced human prostate cancer.

Exploring the role of combined external beam radiotherapy and targeted radioligand therapy with [177Lu]Lu-PSMA-617 for prostate cancer - from bench to bedside

Management of prostate cancer (PC) might be improved by combining external beam radiotherapy (EBRT) and prostate-specific membrane antigen (PSMA)-targeted radioligand therapy (RLT) with lutetium-177 (177Lu)-labeled PSMA inhibitors. We hypothesized a higher efficacy of the combination due to augmentation of the radiation dose to the tumor and interactions of EBRT with PSMA expression potentially increasing radiopharmaceutical uptake. Therefore, this study analyzed the influence of radiation on PSMA expression levels in vitro. The results were translated to evaluate the efficacy of the combination of photon EBRT and [177Lu]Lu-PSMA-617 in a murine PC xenograft model. Finally, a clinical case report on a combined elective field EBRT with RLT dose escalation illustrates a proof-of-concept. Methods: PSMA gene and protein expression were assessed in human PSMA-overexpressing LNCaP cells after irradiation using reverse transcription quantitative polymerase chain reaction (RT-qPCR), flow cytometry and On-Cell Western assays. In the in vivo therapy study, LNCaP tumor-bearing BALB/c nu/nu mice were irradiated once with 2 Gy X-ray EBRT and injected with 40 MBq [177Lu]Lu-PSMA-617 after 4 h or received single or no treatment (n = 10 each). Tumor-absorbed doses by [177Lu]Lu-PSMA-617 were calculated according to the Medical Internal Radiation Dosimetry (MIRD) formalism after deriving time-activity curves using a gamma probe. An exemplified patient case is demonstrated where fractionated EBRT (54 Gy to prostate; 45 Gy to pelvic lymphatics) and three cycles of [177Lu]Lu-PSMA-617 (3.4-6.0 GBq per cycle) were sequentially combined under concurrent androgen deprivation for treating locally advanced PC. Results: At 4 h following irradiation with 2-8 Gy, LNCaP cells displayed a PSMA protein upregulation by around 18% relative to non-irradiated cells, and a stronger upregulation on mRNA level (up to 2.6-fold). This effect was reversed by 24 h when PSMA protein levels were downregulated by up to 22%. Mice treated with the combination therapy showed significantly improved outcomes regarding tumor control and median survival (p < 0.0001) as compared to single or no treatment. Relative to monotherapy with PSMA-RLT or EBRT, the tumor doubling time was prolonged 1.7- or 2.7-fold and the median survival was extended by 24% or 60% with the combination, respectively. Additionally, tumors treated with EBRT exhibited a 14% higher uptake of the radiopharmaceutical as evident from the calculated tumor-absorbed dose, albeit with high variability in the data. Concerning the patient case, the tri-modality treatment was well tolerated and the patient responded with a long-lasting complete biochemical remission for five years following end of PSMA-RLT. The patient then developed a biochemical relapse with oligo-recurrent disease on follow-up imaging. Conclusion: The present preclinical and clinical data demonstrate that the combination of EBRT with dose escalation by PSMA-RLT improves tumor control and potentially prolongs survival. This may pave the way for further clinical investigations of this approach to explore the curative potential of the combination therapy.

In Vivo Evaluation of Brain [18F]F-FDG Uptake Pattern Under Different Anaesthesia Protocols

BACKGROUND/AIM

Since the use of anaesthetics has the drawback of altering radiotracer distribution, preclinical positron emission tomography (PET) imaging findings of anaesthetised animals must be carefully handled. This study aimed at assessing the cerebral [18F]F-FDG uptake pattern in healthy Wistar rats under four different anaesthesia protocols using microPET/magnetic resonance imaging (MRI) examinations.

MATERIALS AND METHODS

Post-injection of 15±1.2 MBq of [18F]F-FDG, either while awake or during the isoflurane-induced incubation phase was applied. Prior to microPET/MRI imaging, one group of the rats was subjected to forane-only anaesthesia while the other group was anaesthetised with the co-administration of forane and dexmedetomidine/Dexdor® Results: While as for the whole brain it was the addition of dexmedetomidine/Dexdor® to the anaesthesia protocol that generated the differences between the radiotracer concentrations of the investigated groups, regarding the cortex, the [18F]F-FDG accumulation was rather affected by the way of incubation. To ensure the most consistent and highest uptake, forane-induced anaesthesia coupled with an awake uptake condition seemed to be most suitable method of anaesthetisation for cerebral metabolic assessment. Diminished whole brain and cortical tracer accumulation detected upon dexmedetomidine/Dexdor® administration highlights the significance of the mechanism of action of different anaesthetics on radiotracer pharmacokinetics.

CONCLUSION

Overall, the standardization of PET protocols is of utmost importance to avoid the confounding factors derived from anaesthesia.

Exploration of radionuclide labeling of a novel scFv-Fc fusion protein targeting CLDN18.2 for tumor diagnosis and treatment

PURPOSE

Claudin 18.2 (CLDN18.2), due to its highly selective expression in tumor cells, has made breakthrough progress in clinical research and is expected to be integrated into routine tumor diagnosis and treatment.

METHODS

In this research, we obtained an scFv-Fc fusion protein (SF106) targeting CLDN18.2 through hybridoma technology. The scFv-Fc fusion protein was labeled with radioactive isotopes (124I and 177Lu) to generate the radio-probes. The targeting and specificity of the radio-probes were tested in cellular models, and its diagnostic and therapeutic potential was further evaluated in tumor-bearing models.

RESULTS

The molecular probes [124I]I-SF106 and [177Lu]Lu-DOTA-SF106 possess high radiochemical purity (RCP, 98.18 ± 0.93 % and 97.05 ± 1.1 %) and exhibit good stability in phosphate buffer saline and 5 % human serum albumin (92.44 ± 4.68 % and 91.03 ± 2.42 % at 120 h). [124I]I-SF106 uptake in cells expressing CLDN18.2 was well targeted and specific, and the dissociation constant was 17.74 nM [124I]I-SF106 micro-PET imaging showed that the maximum standardized uptake value (SUVmax) was significantly higher than CLDN18.2-negative tumors (1.83 ± 0.02 vs. 1.23 ± 0.04, p < 0.001). The maximum uptake was attained in tumors expressing CLDN18.2 at 48 h after injection. [124I]I-SF106 and [177Lu]Lu-DOTA-SF106 dosimetric study showed that the effective dose in humans complies with the medical safety standards required for their clinical application. The results of treatment experiments showed that 3 MBq of [177Lu]Lu-DOTA-SF106 in CLDN18.2-expressing tumor-bearing mice could significantly inhibit tumor growth.

CONCLUSION

These results indicate that radionuclide-labeled scFv-Fc molecular probes ([124I]I-SF106 and [177Lu]Lu-DOTA-SF106) provide a new possibility for the diagnosis and treatment of CLDN18.2-positive cancer patients in clinical practice.

18F- FDG PET/CT in reclassifying the probable diagnosis of IE - A review

In the diagnosis of infective endocarditis (IE), Modified Duke's criteria, coupled with clinical suspicion, serve as the guiding framework. For cases involving prosthetic valve endocarditis and infections affecting implantable devices, the use of metabolic imaging with 18 F-FDG PET/CT scans has gained prominence, as per the recommendations of the European Society of Cardiology guidelines. This imaging modality enhances sensitivity and specificity by identifying infective foci within the heart and extracardiac locations. Early utilization of these scans is crucial for confirming or ruling out IE, although caution is required to mitigate false positive responses, especially in the presence of ongoing inflammatory activity. A standardized ratio of ≥2.0 between FDG uptake around infected tissues and the blood pool has demonstrated a sensitivity of 100 % and specificity of 91 %. It is noteworthy that the sensitivity of FDG PET/CT varies, being lower for native valve and lead infections but considerably higher for prosthetic valve and pulse generator infections. This review provides a comprehensive overview of the advantages offered by FDG PET/CT in achieving a definitive diagnosis of IE.

Biocompatible conjugated polymer nanoparticles labeled with 225Ac for tumor endoradiotherapy

Recently, endoradiotherapy based on actinium-225 (225Ac) has attracted increasing attention, which is due to its α particles can generate maximal damage to cancer cells while minimizing unnecessary radiation effects on healthy tissues. Herein, 111In/225Ac-radiolabeled conjugated polymer nanoparticles (CPNs) coated with amphiphilic polymer DSPE-PEG-DOTA have been developed as a new injectable nano-radiopharmaceuticals for cancer endoradiotherapy under the guidance of nuclear imaging. Single photon emission computed tomography/computed tomography (SPECT/CT) using 111In-DOTA-PEG-CPNs as nano probe indicates a prolonged retention of radiolabeled nanocarriers, which was consistent with the in vivo biodistribution examined by direct radiometry analysis. Significant inhibition of tumor growth has been observed in murine 4T1 models treated with 225Ac-DOTA-PEG-CPNs when compared to mice treated with PBS or DOTA-PEG-CPNs. The 225Ac-DOTA-PEG-CPNs group experienced no single death within 24 days with the median survival considerably extended to 35 days, while all the mice treated with PBS or DOTA-PEG-CPNs died at 20 days post injection. Additionally, the histopathology studies demonstrated no obvious side effects on healthy tissues after treatment with 225Ac-DOTA-PEG-CPNs. All these results reveal that the new 225Ac-labeled DOTA-PEG-CPNs is promising as paradigm for endoradiotherapy.

Next generation fibroblast activation protein (FAP) targeting PET tracers - The tetrazine ligation allows an easy and convenient way to 18F-labeled (4-quinolinoyl)glycyl-2-cyanopyrrolidines

Small-molecular fibroblast activation protein inhibitor (FAPI)-based tracer have been shown to be promising Positron Emission Tomography (PET) 68Ga-labeled radiopharmaceuticals to image a variety of tumors including pancreatic, breast, and colorectal cancers, among others. In this study, we developed a novel 18F-labeled FAPI derivative. [18F]6 was labeled using a synthon approach based on the tetrazine ligation. It showed subnanomolar affinity for the FAP protein and a good selectivity profile against known off-target proteases. Small animal PET studies revealed high tumor uptake and good target-to-background ratios. [18F]6 was excreted via the liver. Overall, [18F]6 showed promising characteristics to be used as a PET tracer and could serve as a lead for further development of halogen-based theranostic FAPI radiopharmaceuticals.

Prevention of activated brown adipose tissue on 18F-FDG-PET scans of young lymphoma patients: results of an ancillary study within the EuroNet-PHL-C2 trial

Activated brown fat (aBAT) is known to affect the evaluation of 18F-FDG PET scans, especially in young patients. The aim of this study was to determine factors influencing the occurrence of aBAT, and to investigate the effectiveness of the two preventive measures, warming and beta-blocker (propranolol) administration. Five-hundred-twenty-eight 18F-FDG-PET scans of 241 EuroNet-PHL-C2 trial patients from 41 nuclear medicine departments in Germany and Czech Republic were screened for aBAT. The occurrence of aBAT was analyzed with patient characteristics (age, sex, body mass index, predisposition to aBAT), weather data at the day of 18F-FDG PET scanning as well as the preventive measures taken. Potentially important factors from univariate analyses were included into a logistic regression model. Warming as a preventive measure was used in 243 18F-FDG-PET scans, propranolol was administered in 36, warming and propranolol were combined in 84, and no preventive measures were taken in 165 scans. Whereas age, sex and body mass index had no clear impact, there was an individual predisposition to aBAT. Logistic regression model revealed that the frequency of aBAT mainly depends on the outside temperature (p = 0.005) and can be effectively reduced by warming (p = 0.004), the administration of unselective beta-blocker or the combination of both. Warming is a simple, cheap and non-invasive method to reduce the frequency of aBAT. However, the effect of warming decreases with increasing outside temperatures. Administration of propranolol seems to be equally effective and provides advantages whenever the positive effect of warming is compromised. The combination of both preventive measures could have an additive effect.

177 Lu Radiolabelled AIE Dots for Multimodal Imaging Guided Photothermal/Radiopharmaceutical Tumor Therapy

Aggregation-induced emission luminogens (AIEgens) in the second near-infrared region (NIR-II,1000-1700 nm) have shown tremendous potential as theragnostic probe for tumor multimodal diagnostic imaging and combined treatment owing to their programmable optical, structural and functional properties. Herein, we presented a radionuclide 177 Lu-labeled AIEgen, 177 Lu-2TT-oC6B dots, for NIR-II fluorescence and SPECT/CT imaging-guided tumor photothermal and radiopharmaceutical therapy. Intriguingly, 177 Lu-2TT-oC6B self-assembled into 10 nm dots, exhibited high NIR-II fluorescence quantum yield (QY, 1.34 %) and unprecedented photothermal conversion efficiency (PCE, 70.3 %) in vitro, furtherly performed extremely long blood circulation (T1/2 =52.4 h), persistent tumor accumulation and retention in tumor (NIR-II SNR=5.56; SPECT SNR=36.59) via intravenous administration in vivo. Furthermore, upon NIR light activation and 177 Lu irradiation, 177 Lu-2TT-oC6B demonstrated great application potential in synergistic photothermal/radiopharmaceutical tumor therapy.

Reappraisal of [18F]FDG-PET/CT for diagnosis and management of cardiac implantable electronic device infections

INTRODUCTION AND OBJECTIVES

The role of [18F]FDG-PET/CT in cardiac implantable electronic device (CIED) infections requires better evaluation, especially in the diagnosis of systemic infections. We aimed to determine the following: a) the diagnostic accuracy of [18F]FDG-PET/CT in each CIED topographical region, b) the added value of [18F]FDG-PET/CT over transesophageal echocardiography (TEE) in diagnosing systemic infections, c) spleen and bone marrow uptake in differentiating isolated local infections from systemic infections, and d) the potential application of [18F]FDG-PET/CT in follow-up.

METHODS

Retrospective single-center study including 54 cases and 54 controls from 2014 to 2021. The Primary endpoint was the diagnostic yield of [18F]FDG-PET/CT in each topographical CIED region. Secondary analyses described the performance of [18F]FDG-PET/CT compared with that of TEE in systemic infections, bone marrow and spleen uptake in systemic and isolated local infections, and the potential application of [18F]FDG-PET/CT in guiding cessation of chronic antibiotic suppression when completed device removal is not performed.

RESULTS

We analyzed 13 (24%) isolated local infections and 41 (76%) systemic infections. Overall, the specificity of [18F]FDG-PET/CT was 100% and sensitivity 85% (79% pocket, 57% subcutaneous lead, 22% endovascular lead, 10% intracardiac lead). When combined with TEE, [18F]FDG-PET/CT increased definite diagnosis o fsystemic infections from 34% to 56% (P=.04). Systemic infections with bacteremia showed higher spleen (P=.05) and bone marrow metabolism (P=.04) than local infections. Thirteen patients without complete device removal underwent a follow-up [18F]FDG-PET/CT, with no relapses after discontinuation of chronic antibiotic suppression in 6 cases with negative follow-up [18F]FDG-PET/CT.

CONCLUSIONS

The sensitivity of [18F]FDG-PET/CT for evaluating CIED infections was high in local infections but much lower in systemic infections. However, accuracy increased when [18F]FDG-PET/CT was combined with TEE in endovascular lead bacteremic infection. Spleen and bone marrow hypermetabolism could differentiate bacteremic systemic infection from local infection. Although further prospective studies are needed, follow-up [18F]FDG-PET/CT could play a potential role in the management of chronic antibiotic suppression therapy when complete device removal is unachievable.

Design, Synthesis, and Evaluation of 18F-Labeling CYP1B1 PET Tracer Based on 2-Phenylquinazolin

Cytochrome P450 (CYP)1B1 has been identified to be specifically overexpressed in several solid tumors, thus it's a potential target for the detection of tumors. Based on the 2-Phenylquinazolin CYP1B1 inhibitors, we designed and synthesized several positron emission computed tomography (PET) imaging probes targeting CYP1B1. Through IC50 determinations, most of these probes exhibited good affinity and selectivity to CYP1B1. Considering their affinity, solubility, and their 18F labeling methods, we chose compound 5c as the best candidate. The 18F radiolabeling of [18F] 5c was easy to handle with good radiolabeling yield and radiochemical purity. In vitro and in vivo stability study indicated that probe [18F]5c has good stability. In cell binding assay, [18F]5c could be specifically taken up by tumor cells, especially HCT-116 cells. Although the tumor-blood (T/B) and tumor-muscle (T/M) values and PET imaging results were unsatisfied, it is still possible to develop PET probes targeting CYP1B1 by structural modification on the basis of 5c in the future.

Radiopharmaceuticals as combinatorial partners for immune checkpoint inhibitors

Immune checkpoint inhibitors (ICIs) have revolutionized the treatment of multiple cancer types. However, only a fraction of patients with cancer responds to ICIs employed as stand-alone therapeutics, calling for the development of safe and effective combinatorial regimens to extend the benefits of ICIs to a larger patient population. In addition to exhibiting a good safety and efficacy profile, targeted radionuclide therapy (TRT) with radiopharmaceuticals that specifically accumulate in the tumor microenvironment has been associated with promising immunostimulatory effects that (at least in preclinical cancer models) provide a robust platform for the development of TRT/ICI combinations. We discuss preclinical and clinical findings suggesting that TRT stands out as a promising partner for the development of safe and efficient combinatorial regimens involving ICIs.

In silico evaluation of new mangiferin-based Positron Emission Tomography radiopharmaceuticals through the inhibition of metalloproteinase-9

Metalloproteinase-9 (MMP-9) is a key protein in cancer advancement and metastasis owing to its ability to degrade some extracellular matrix components. Mangiferin, a natural polyphenolic compound, has demonstrated through experimental and theoretical studies to be a great anticancer agent for the selective inhibition of MMP-9. This work aimed to evaluate the utility of several fluorinated compounds obtained from MF as possible Positron Emission Tomography (PET) radiopharmaceuticals oriented to MMP-9. Density Functional Theory calculations of MF were made to obtain the most active sites toward electrophilic and nucleophilic reactions and propose a synthetic route to produce its fluorinated derivatives. The reactivity study allowed us to propose a late-stage synthetic route based on click chemistry to obtain three fluorinated MF-based derivatives. Molecular docking calculations suggested that the derivative F-propyl-MF could be suitable as PET radiopharmaceutical owing to the establishment of a five-coordinated complex with the catalytic Zn atom belonging to the active site of MMP-9, crucial factor in the inhibition of MMP-9.

[18F]FDG PET/MRI in children suffering from lymphoma: does MRI contrast media make a difference?

OBJECTIVES

Evaluate the influence of an MRI contrast agent application on primary and follow-up staging in pediatric patients with newly diagnosed lymphoma using [18F]FDG PET/MRI to avoid adverse effects and save time and costs during examination.

METHODS

A total of 105 [18F]FDG PET/MRI datasets were included for data evaluation. Two different reading protocols were analyzed by two experienced readers in consensus, including for PET/MRI-1 reading protocol unenhanced T2w and/or T1w imaging, diffusion-weighted imaging (DWI), and [18F]FDG PET imaging and for PET/MRI-2 reading protocol an additional T1w post contrast imaging. Patient-based and region-based evaluation according to the revised International Pediatric Non-Hodgkin's Lymphoma (NHL) Staging System (IPNHLSS) was performed, and a modified standard of reference was applied comprising histopathology and previous and follow-up cross-sectional imaging. Differences in staging accuracy were assessed using the Wilcoxon and McNemar tests.

RESULTS

In patient-based analysis, PET/MRI-1 and PET/MRI-2 both determined a correct IPNHLSS tumor stage in 90/105 (86%) exams. Region-based analysis correctly identified 119/127 (94%) lymphoma-affected regions. Sensitivity, specificity, positive predictive value, negative predictive value, and diagnostic accuracy for PET/MRI-1 and PET/MRI-2 were 94%, 97%, 90%, 99%, 97%, respectively. There were no significant differences between PET/MRI-1 and PET/MRI-2.

CONCLUSIONS

The use of MRI contrast agents in [18F]FDG PET/MRI examinations has no beneficial effect in primary and follow-up staging of pediatric lymphoma patients. Therefore, switching to a contrast agent-free [18F]FDG PET/MRI protocol should be considered in all pediatric lymphoma patients.

CLINICAL RELEVANCE STATEMENT

This study gives a scientific baseline switching to a contrast agent-free [18F]FDG PET/MRI staging in pediatric lymphoma patients. This could avoid side effects of contrast agents and saves time and costs by a faster staging protocol for pediatric patients.

KEY POINTS

• No additional diagnostic benefit of MRI contrast agents at [18F]FDG PET/MRI examinations of pediatric lymphoma primary and follow-up staging • Highly accurate primary and follow-up staging of pediatric lymphoma patients at MRI contrast-free [18F]FDG PET/MRI.

Flurpiridaz F-18 PET Myocardial Perfusion Imaging in Patients With Suspected Coronary Artery Disease

BACKGROUND

Flurpiridaz F-18 (flurpiridaz) is a novel positron emission tomography (PET) myocardial perfusion imaging tracer.

OBJECTIVES

The purpose of this study was to further assess the diagnostic efficacy and safety of flurpiridaz for the detection and evaluation of coronary artery disease (CAD) defined as ≥50% stenosis by quantitative invasive coronary angiography (ICA).

METHODS

In this second phase 3 prospective multicenter clinical study, 730 patients with suspected CAD from 48 clinical sites in the United States, Canada, and Europe were enrolled. Patients underwent 1-day rest/stress flurpiridaz PET and 1- or 2-day rest-stress Tc-99m-labeled single photon emission computed tomography (SPECT) before ICA. PET and SPECT images were read by 3 experts blinded to clinical and ICA data.

RESULTS

A total of 578 patients (age 63.7 ± 9.5 years) were evaluable; 32.5% were women, 52.3% had body mass index ≥30 kg/m2, and 33.6% had diabetes. Flurpiridaz PET met the efficacy endpoints of the study; its sensitivity and specificity were significantly higher than the prespecified threshold value by 2 of the 3 readers. The sensitivity of flurpiridaz PET was higher than SPECT (80.3% vs 68.7%; P = 0.0003) and its specificity was noninferior to SPECT (63.8% vs 61.7%; P = 0.0004). PET area under the receiver-operating characteristic curves were higher than SPECT in the overall population (0.80 vs 0.68; P < 0.001), women, and obese patients (P < 0.001 for both). Flurpiridaz PET was superior to SPECT (P < 0.001) for perfusion defect size/severity evaluation, image quality, diagnostic certainty, and radiation exposure. Flurpiridaz PET was safe and well tolerated.

CONCLUSIONS

This second flurpiridaz PET myocardial perfusion imaging trial shows that flurpiridaz has utility as a new tracer for CAD detection, specifically in women and obese patients. (An International Study to Evaluate Diagnostic Efficacy of Flurpiridaz [18F] Injection PET MPI in the Detection of Coronary Artery Disease [CAD]; NCT03354273).

Synthesis of novel DOTA-/AAZTA-based bifunctional chelators: Solution thermodynamics, peptidomimetic conjugation, and radiopharmaceutical evaluation

Bifunctional chelators (BFCs), which link metallic radionuclide and a targeting vector, are some of the most crucial components of metallic radionuclide-based radiopharmaceuticals for positron-emission computed tomography (PET) imaging. In this study, we designed and synthesized two versatile BFCs, p-NCS-Ph-DE4TA and p-NCS-Ph-AAZ4TA, and we conjugated them with a prostate-specific membrane antigen (PSMA) inhibitor. These two chelators showed high affinity for Ga (III) according to a study of the thermodynamics and kinetics and DFT calculations. The labeled PSMA targeted probes, [68Ga]Ga-p-NCS-Ph-DE4TA-PSMA and [68Ga]Ga-p-NCS-Ph-AAZ4TA-PSMA, maintained excellent stability in vitro, and they exhibited high specific activity when binding to PSMA. A PET/CT imaging study in mice bearing SMMC-7721 hepatocellular carcinoma xenografts demonstrated clear visualization of tumors with a high tumor uptake and low background level, indicating the excellent performance in vivo and specific activity when targeting hepatocellular carcinomas. In summary, p-NCS-Ph-DE4TA and p-NCS-Ph-AAZ4TA are leading developmental candidates for PET imaging for tumor diagnosis.

Towards a fast PET/MRI protocol for breast cancer imaging: maintaining diagnostic confidence while reducing PET and MRI acquisition times

OBJECTIVES

To investigate the diagnostic feasibility of a shortened breast PET/MRI protocol in breast cancer patients.

METHODS

Altogether 90 women with newly diagnosed T1tumor-staged (T1ts) and T2tumor-staged (T2ts) breast cancer were included in this retrospective study. All underwent a dedicated comprehensive breast [18F]FDG-PET/MRI. List-mode PET data were retrospectively reconstructed with 20, 15, 10, and 5 min for each patient to simulate the effect of reduced PET acquisition times. The SUVmax/mean of all malign breast lesions was measured. Furthermore, breast PET data reconstructions were analyzed regarding image quality, lesion detectability, signal-to-noise ratio (SNR), and image noise (IN). The simultaneously acquired comprehensive MRI protocol was then shortened by retrospectively removing sequences from the protocol. Differences in malignant breast lesion detectability between the original and the fast breast MRI protocol were evaluated lesion-based. The 20-min PET reconstructions and the original MRI protocol served as reference.

RESULTS

In all PET reconstructions, 127 congruent breast lesions could be detected. Group comparison and T1ts vs. T2ts subgroup comparison revealed no significant difference of subjective image quality between 20, 15, 10, and 5 min acquisition times. SNR of qualitative image evaluation revealed no significant difference between different PET acquisition times. A slight but significant increase of IN with decreasing PET acquisition times could be detected. Lesion SUVmax group comparison between all PET acquisition times revealed no significant differences. Lesion-based evaluation revealed no significant difference in breast lesion detectability between original and fast breast MRI protocols.

CONCLUSIONS

Breast [18F]FDG-PET/MRI protocols can be shortened from 20 to below 10 min without losing essential diagnostic information.

KEY POINTS

• A highly accurate breast cancer evaluation is possible by the shortened breast [18F]FDG-PET/MRI examination protocol. • Significant time saving at breast [18F]FDG-PET/MRI protocol could increase patient satisfaction and patient throughput for breast cancer patients at PET/MRI.

Pre-discharge 18F-Flourodeoxyglucose uptake pattern following transcatheter aortic-valve replacement and adverse prognostic features in aortic stenosis

18F-Flourodeoxyglucose positron emission tomography/computed tomography (18F-FDG-PET/CT) has been shown to be of utility in transcatheter aortic valve replacement (TAVR) patients with suspected prosthetic valve endocarditis. In the present study, we sought to analyze the relationship between 18F-FDG-PET/CT performed before discharge in TAVR patients and adverse prognostic features of aortic stenosis. We analyzed the association between 18F-FDG-PET/CT uptake pattern and degree of left ventricular mass index, aortic root dilatation, and aortic leaflet calcification extent. This is the first study to demonstrate that pre-discharge 18F-FDG-PET/CT in patients undergoing TAVR shows a significant negative correlation between 18F-FDG uptake pattern and adverse prognostic features.

Diterpenoids with an unusual tricyclo[10.3.0.02,9]pentadecane skeleton from Pedilanthus tithymaloides as multidrug resistance modulators

Three new diterpenoids with an unusual carbon skeleton, pedilanins A-C (1-3), and nine new jatrophane diterpenoids, pedilanins D-L (4-12), along with five known ones (13-17), were isolated from Pedilanthus tithymaloides. Compounds 1-3 characterize an unprecedented tricyclo[10.3.0.02,9]pentadecane skeleton. Compounds 4-8 are rare examples of the jatrophanes bearing a cyclic hemiketal substructure. Their structures were determined by an extensive analysis of HRESIMS, NMR, quantum-chemical calculation, DP4+ probability, and X-ray crystallographic data. In the bioassay, compounds 1-12 dramatically reversed multidrug resistance in cancer cells with the fold-reversals ranging from 17.9 to 396.8 at the noncytotoxic concentration of 10 μM. The mechanism results indicated that compounds 2 and 3 inhibited the P-glycoprotein (Pgp) transporter function, thus reversing the drug resistance.

Hybrid simultaneous whole-body 2-[18F]FDG-PET/MRI imaging in newly diagnosed multiple myeloma: first diagnostic performance and clinical added value results

OBJECTIVES

Mixing diagnostic and prognostic data provided by whole-body MRI (WB-MRI) and 2-18F-fluorodeoxyglucose (2-[18F]FDG) positron emission tomography (2-[18F]FDG-PET) from a single simultaneous imaging technique for newly diagnosed multiple myeloma (NDMM) initial workup seems attractive. However, to date, the published data are scarce and this possibility has not been fully explored. In this prospective study, we aimed to explore the diagnostic performance and added clinical value of WB-2-[18F]FDG-PET/MRI imaging in NDMM.

METHODS

All patients with confirmed NDMM at the Nantes University Hospital were prospectively enrolled in this study and underwent WB-2-[18F]FDG-PET/MRI imaging on a 3-T Biograph mMR before receiving treatment. Before imaging, they were considered either as symptomatic or as smoldering MM (SMM). Diagnostic performance of global WB-2-[18F]FDG-PET/MRI imaging, as well as PET and MRI separately for FL and diffuse BMI detection, was assessed and compared in each group. PET-based (maximal standardized uptake value, SUVmax) and MRI-based (mean apparent diffusion coefficient value, ADCmean) quantitative features were collected for FL/para-medullary disease (PMD)/bone marrow and were compared.

RESULTS

A total of 52 patients were included in this study. PET and MRI were equally effective at detecting patients with FL (69% vs. 75%) and with diffuse BMI (62% for both) in the symptomatic MM group. WB-2-[18F]FDG-PET/MRI imaging detected FL in 22% of patients with SMM (with a higher diagnostic performance for MRI), resulting in a significant impact on clinical management in this population. SUVmax and ADCmean quantitative features were weakly or not correlated.

CONCLUSIONS

WB-2-[18F]FDG-PET/MRI could represent the next-generation imaging modality for MM.

KEY POINTS

• Whole-body 2-[18F]FDG-PET/MRI imaging detected at least one focal bone lesion in 75% of patients with symptomatic multiple myeloma, and PET and MRI were equally effective at identifying patients with a focal bone lesion. • Whole-body 2-[18F]FDG-PET/MRI imaging detected a focal bone lesion in 22% of patients with smoldering multiple myeloma (with a higher diagnostic performance for MRI). • MRI had a significant impact on clinical management of smoldering multiple myeloma.

Recent Advances in Bioorthogonal Click Chemistry for Enhanced PET and SPECT Radiochemistry

Due to their high reaction rate and reliable selectivity, bioorthogonal click reactions have been extensively investigated in numerous research fields, such as nanotechnology, drug delivery, molecular imaging, and targeted therapy. Previous reviews on bioorthogonal click chemistry for radiochemistry mainly focus on ¹⁸F-labeling protocols employed to produce radiotracers and radiopharmaceuticals. In fact, besides fluorine-18, other radionuclides such as gallium-68, iodine-125, and technetium-99m are also used in the field of bioorthogonal click chemistry. Herein, to provide a more comprehensive perspective, we provide a summary of recent advances in radiotracers prepared using bioorthogonal click reactions, including small molecules, peptides, proteins, antibodies, and nucleic acids as well as nanoparticles based on these radionuclides. The combination of pretargeting with imaging modalities or nanoparticles, as well as the clinical translations study, are also discussed to illustrate the effects and potential of bioorthogonal click chemistry for radiopharmaceuticals.

Imaging DNA damage response by γH2AX in vivo predicts treatment response to Lutetium-177 radioligand therapy and suggests senescence as a therapeutically desirable outcome

Rationale: An effective absorbed dose response relationship is yet to be established for Lutetium-177 based radionuclide therapies such as 177Lu-DOTATATE and 177Lu-PSMA. The inherent biological heterogeneity of neuroendocrine and prostate cancers may make the prospect of establishing cohort-based dose-response relationships unobtainable. Instead, an individual-based approach, monitoring the dose-response within each tumor could provide the necessary metric to monitor treatment efficacy. Methods: We developed a dual isotope SPECT imaging strategy to monitor the change over time in the relationship between 177Lu-DOTATATE and 111In-anti-γH2AX-TAT, a modified radiolabelled antibody that allows imaging of DNA double strand breaks, in mice bearing rat pancreatic cancer xenografts. The dynamics of γH2AX foci, apoptosis and senescence following exposure to 177Lu-DOTATATE was further investigated in vitro and in ex vivo tumor sections. Results: The change in slope of the 111In-anti-γH2AX-TAT to 177Lu signal between days 5 and 7 was found to be highly predictive of survival (r = 0.955, P < 0.0001). This pivotal timeframe was investigated further in vitro: clonogenic survival correlated with the number of γH2AX foci at day 6 (r = -0.995, P < 0.0005). While there was evidence of continuously low levels of apoptosis, delayed induction of senescence in vitro appeared to better account for the γH2AX response to 177Lu. The induction of senescence was further investigated by ex vivo analysis and corresponded with sustained retention of 177Lu within tumor regions. Conclusions: Dual isotope SPECT imaging can provide individualized tumor dose-responses that can be used to predict lutetium-177 treatment efficacy. This bio-dosimeter metric appears to be dependent upon the extent of senescence induction and suggests an integral role that senescence plays in lutetium-177 treatment efficacy.

Somatostatin Receptor PET/MR Imaging of Inflammation in Patients With Large Vessel Vasculitis and Atherosclerosis

BACKGROUND

Assessing inflammatory disease activity in large vessel vasculitis (LVV) can be challenging by conventional measures.

OBJECTIVES

We aimed to investigate somatostatin receptor 2 (SST2) as a novel inflammation-specific molecular imaging target in LVV.

METHODS

In a prospective, observational cohort study, in vivo arterial SST2 expression was assessed by positron emission tomography/magnetic resonance imaging (PET/MRI) using 68Ga-DOTATATE and 18F-FET-βAG-TOCA. Ex vivo mapping of the imaging target was performed using immunofluorescence microscopy; imaging mass cytometry; and bulk, single-cell, and single-nucleus RNA sequencing.

RESULTS

Sixty-one participants (LVV: n = 27; recent atherosclerotic myocardial infarction of ≤2 weeks: n = 25; control subjects with an oncologic indication for imaging: n = 9) were included. Index vessel SST2 maximum tissue-to-blood ratio was 61.8% (P < 0.0001) higher in active/grumbling LVV than inactive LVV and 34.6% (P = 0.0002) higher than myocardial infarction, with good diagnostic accuracy (area under the curve: ≥0.86; P < 0.001 for both). Arterial SST2 signal was not elevated in any of the control subjects. SST2 PET/MRI was generally consistent with 18F-fluorodeoxyglucose PET/computed tomography imaging in LVV patients with contemporaneous clinical scans but with very low background signal in the brain and heart, allowing for unimpeded assessment of nearby coronary, myocardial, and intracranial artery involvement. Clinically effective treatment for LVV was associated with a 0.49 ± 0.24 (standard error of the mean [SEM]) (P = 0.04; 22.3%) reduction in the SST2 maximum tissue-to-blood ratio after 9.3 ± 3.2 months. SST2 expression was localized to macrophages, pericytes, and perivascular adipocytes in vasculitis specimens, with specific receptor binding confirmed by autoradiography. SSTR2-expressing macrophages coexpressed proinflammatory markers.

CONCLUSIONS

SST2 PET/MRI holds major promise for diagnosis and therapeutic monitoring in LVV. (PET Imaging of Giant Cell and Takayasu Arteritis [PITA], NCT04071691; Residual Inflammation and Plaque Progression Long-Term Evaluation [RIPPLE], NCT04073810).

A Novel Tumor Hypoxia Imaging Agent: [99mTc]Tc(CO)3-CPA-2-NIM

INTRODUCTION

Hypoxia imaging agents can selectively remain in hypoxic tissue, which can directly reflect the location and degree of hypoxia.

METHODS

Synthesized a novel tumor hypoxia imaging probe [99mTc]Tc(CO)3-CPA-2-NIM and evaluated its biological behavior with the purpose to assess its possibility of becoming a qualified tumor hypoxia imaging agent.

RESULTS

Radiochemcial purity of [99mTc]Tc(CO)3-CPA-2-NIM was greater than 95% after HPLC purification. Lipophilicity coefficient of this complex was -1.74 ± 0.10 (n = 5, number of experiments), indicating it was a hydrophilic complex. In vitro cell experiments demonstrated that this complex has selectivity for hypoxia at oxygen concentrations < 10 ppm (parts per million). Biodistribution experiment in S180 tumor bearing mice showed that tumor uptake reached its highest at 2 h post-injection with mice tumor-to-muscle ratio.

CONCLUSIONS

Complex [99mTc]Tc(CO)3-CPA-2-NIM has the possibility of becoming a tumor hypoxia imaging agent.

Light Chain Testing Abnormalities Among Patients With Transthyretin Amyloid Cardiomyopathy Referred for Technetium-99m Pyrophosphate Imaging

Clinical algorithms stipulate that transthyretin amyloid cardiomyopathy (ATTR-CM) can be diagnosed noninvasively by technetium-99m pyrophosphate (PYP) imaging when light chain (AL) amyloidosis has been excluded. We sought to define the distribution of light chain abnormalities and final diagnosis of ATTR-CM among patients referred for PYP imaging. We conducted a retrospective cohort study of 378 sequential patients with suspected ATTR-CM, referred for PYP imaging from October 2014 to January 2019. PYP scans were adjudicated as per guidelines. We found that 97 patients (26%) had abnormal plasma cell dyscrasia (PCD) markers, including serum free light chain (FLC) and/or urine/serum immunofixation electrophoresis (IFE). After exclusions for incomplete data or known AL amyloidosis, the final study population with abnormal PCD testing was n = 82. Final adjudication of amyloidosis was determined by multidisciplinary clinical assessment and/or tissue biopsy. The median age of cohort was 75 (68 to 81) years, 88% were men, and 33% were Black. Of the 82 patients, 62 had positive PYP scans (76%) and 20 had negative PYP scans (24%). A total of 64 patients had adjudicated ATTR-CM, confirmed by tissue biopsy in 41 (64%). Of those with confirmed ATTR-CM, 44 (69%) had abnormal FLC ratio between 1.65 and 3.1 and normal IFE. In conclusion, among patients referred for technetium-99m-PYP imaging for suspected ATTR-CM, 26% exhibited abnormalities of PCD markers. An FLC ratio 1.65 to 3.1, with normal IFE was noted in 69% of those with ATTR-CM, suggesting that ATTR-CM can be diagnosed noninvasively without cardiac biopsy in patients with positive PYP scan and similar plasma cell testing results.

Measurement of Hepatic CYP3A4 and 2D6 Activity Using Radioiodine-Labeled O-Desmethylvenlafaxine

Drug metabolizing enzyme activity is affected by various factors such as drug–drug interactions, and a method to quantify drug metabolizing enzyme activity in real time is needed. In this study, we developed a novel radiopharmaceutical for quantitative imaging to estimate hepatic CYP3A4 and CYP2D6 activity. Iodine-123- and 125-labeled O-desmethylvenlafaxine (123/125I-ODV) was obtained with high labeling and purity, and its metabolism was found to strongly involve CYP3A4 and CYP2D6. SPECT imaging in normal mice showed that the administered 123I-ODV accumulated early in the liver and was excreted into the gallbladder, as evaluated by time activity curves. In its biological distribution, 125I-ODV administered to mice accumulated early in the liver, and only the metabolite of 125I-ODV was quickly excreted into the bile. In CYP3A4- and CYP2D6-inhibited model mice, the accumulation in bile decreased more than in normal mice, indicating inhibition of metabolite production. These results indicated that imaging and quantifying the accumulation of radioactive metabolites in excretory organs will aid in determining the dosages of various drugs metabolized by CYP3A4 and CYP2D6 for individualized medicine. Thus, 123/125I-ODV has the potential to direct, comprehensive detection and measurement of hepatic CYP3A4 and CYP2D6 activity by a simple and less invasive approach.

The preparation, biodistribution, and human's absorbed dose evaluation of Radio-Scandium-HYNIC-TOC for somatostatin-receptor-positive neuroendocrine tumors therapy by animal study

BACKGROUND

Most of the neuroendocrine tumors (NETs) express Somatostatin receptors (SSTr), which are the main bases for the development of several radiopharmaceuticals for therapy and imaging of these types of tumors. In this study, 46 Scandium nuclide was used to label a peptide compound via hydrazinonicotinyl-Tyr3-Octreotide (HYNIC-TOC) and researched further for somatostatin-receptor NETs treatment.

METHODS AND MATERIALS

The labeling procedure was conducted at 95°C for 10 min. The compound stability was tested in the environment of human serum at 37°C. The biodistribution of compound was investigated in balb/c normal mice and mice bearing AR4-2J tumor. Absorbed Doses of Human Organs were estimated by extrapolation of the biokinetics data of compound in mice to human's organs and then the absorbed doses were estimated by application of MATLAB and MIRDOSE software.

RESULTS

Labeling yield was more than 90% with 555 MBq/mg specific activity. The radio-labeled compound expressed well consistency in human serum. The tumor uptake reached 3.831 ID/g% until 4 h post-injection and increased to 5.564%ID/g until 24 h post-injection.

CONCLUSION

The main achievement of this study was high tumor uptake of 46 Sc-HYNIC-TOC which may be therapeutically valuable for the therapy of NETs. The estimation of the absorbed dose of human from 47 Scandium-HYNIC-TOC showed low absorbed doses in critical organs and the elimination of the radiopharmaceutical was through the gastrointestinal tract.

Diagnostic Accuracy of 2-[18F]FDG-PET and whole-body DW-MRI for the detection of bone marrow metastases in children and young adults

OBJECTIVES

To compare the diagnostic accuracy of 2-[18F]fluoro-2-deoxy-D-glucose-enhanced positron emission tomography (2-[18F]FDG-PET) and diffusion-weighted magnetic resonance imaging (DW-MRI) for the detection of bone marrow metastases in children and young adults with solid malignancies.

METHODS

In this cross-sectional single-center institutional review board-approved study, we investigated twenty-three children and young adults (mean age, 16.8 years ± 5.1 [standard deviation]; age range, 7-25 years; 16 males, 7 females) with 925 bone marrow metastases who underwent 66 simultaneous 2-[18F]FDG-PET and DW-MRI scans including 23 baseline scans and 43 follow-up scans after chemotherapy between May 2015 and July 2020. Four reviewers evaluated all foci of bone marrow metastasis on 2-[18F]FDG-PET and DW-MRI to assess concordance and measured the tumor-to-bone marrow contrast. Results were assessed with a one-sample Wilcoxon test and generalized estimation equation. Bone marrow biopsies and follow-up imaging served as the standard of reference.

RESULTS

The reviewers detected 884 (884/925, 95.5%) bone marrow metastases on 2-[18F]FDG-PET and 893 (893/925, 96.5%) bone marrow metastases on DW-MRI. We found different "blind spots" for 2-[18F]FDG-PET and MRI: 2-[18F]FDG-PET missed subcentimeter lesions while DW-MRI missed lesions in small bones. Sensitivity and specificity were 91.0% and 100% for 18F-FDG-PET, 89.1% and 100.0% for DW-MRI, and 100.0% and 100.0% for combined modalities, respectively. The diagnostic accuracy of combined 2-[18F]FDG-PET/MRI (100.0%) was significantly higher compared to either 2-[18F]FDG-PET (96.9%, p < 0.001) or DW-MRI (96.3%, p < 0.001).

CONCLUSIONS

Both 2-[18F]FDG-PET and DW-MRI can miss bone marrow metastases. The combination of both imaging techniques detected significantly more lesions than either technique alone.

KEY POINTS

• DW-MRI and 2-[18F]FDG-PET have different strengths and limitations for the detection of bone marrow metastases in children and young adults with solid tumors. • Both modalities can miss bone marrow metastases, although the "blind spot" of each modality is different. • A combined PET/MR imaging approach will achieve maximum sensitivity and specificity for the detection of bone marrow metastases in children with solid tumors.

Measurement of Blood-Brain Barrier Disruption in Mice Following Ozone Exposure Using Highly Sensitive Radiotracer Assays

Ozone is a widespread air toxicant. Although its primary target organ is the lungs, emerging evidence suggests that ozone also has harmful effects on the brain. The vascular blood-brain barrier (BBB), an endothelial interface that regulates passage of substances between the brain and peripheral tissues, is a likely mediator of ozone's adverse effects on the brain. Ozone can cause BBB disruption, a pathological state in which the BBB becomes leaky, resulting in the unregulated entry of circulating substances into the brain. BBB disruption can be detected using many methods, which each have their strengths and limitations. Recent data suggest that BBB disruption can occur in mice following ozone exposures, albeit at a low level. Therefore, robust and highly sensitive assays for BBB disruption are needed. Assays commonly used to detect BBB disruption, however, can be time consuming, lack sensitivity, and can be vulnerable to artifacts that are typically not addressed in the experimental design. Radiochemical assays are among the most sensitive and specific for detecting subtle disruptions of the BBB and require minimal sample processing for detection. Radiochemical assays can also be multiplexed to include radiotracer conjugates of large and small molecular weights, and the uptake of each of them can provide information about the severity and mechanism of BBB disruption. Here, we describe a protocol to use two of these radiotracer conjugates, ¹⁴ C-sucrose and ^99m Tc- albumin, to measure BBB disruption following an acute exposure to ozone in mice. We provide the steps to expose mice acutely to ozone, to label albumin with ^99m Tc-pertechnetate, and to measure BBB disruption by evaluating permeability to ^99m Tc-albumin and ¹⁴ C-sucrose after ozone exposure. These methods can be adapted to different ozone exposure paradigms and to different rodent species/strains, allowing for the sensitive and rapid assessment of BBB disruption that is detectable in whole brains or in brain regions. © 2022 Wiley Periodicals LLC. Basic Protocol 1: Ozone exposures in mice Basic Protocol 2: Measurement of blood-brain barrier disruption by evaluating permeability to ¹⁴ C-sucrose and ^99m Tc-albumin Support Protocol: Labeling of bovine serum albumin with ^99m Tc.

Mechanoporation enables rapid and efficient radiolabeling of stem cells for PET imaging

Regenerative medicine uses the patient own stem cells to regenerate damaged tissues. Molecular imaging techniques are commonly used to image the transplanted cells, either right after surgery or at a later time. However, few techniques are fast or straightforward enough to label cells intraoperatively. Adipose tissue-derived stem cells (ADSCs) were harvested from knee joints of minipigs. The cells were labeled with PET contrast agent by flowing mechanoporation using a microfluidic device. While flowing through a series of microchannels, cells are compressed repeatedly by micro-ridges, which open transient pores in their membranes and induce convective transport, intended to facilitate the transport of 68Ga-labeled and lipid-coated mesoporous nanoparticles (MSNs) into the cells. This process enables cells to be labeled in a matter of seconds. Cells labeled with this approach were then implanted into cartilage defects, and the implant was imaged using positron emission tomography (PET) post-surgery. The microfluidic device can efficiently label millions of cells with 68Ga-labeled MSNs in as little as 15 min. The method achieved labeling efficiency greater than 5 Bq/cell on average, comparable to 30 min-long passive co-incubation with 68Ga-MSNs, but with improved biocompatibility due to the reduced exposure to ionizing radiation. Labeling time could also be accelerated by increasing throughput through more parallel channels. Finally, as a proof of concept, ADSCs were labeled with 68Ga-MSNs and quantitatively assessed using clinical PET/MR in a mock transplant operation in pig knee joints. MSN-assisted mechanoporation is a rapid, effective and straightforward approach to label cells with 68Ga. Given its high efficiency, this labeling method can be used to track small cells populations without significant effects on viability. The system is applicable to a variety of cell tracking studies for cancer therapy, regenerative therapy, and immunotherapy.

Gastroenteropancreatic grade 3 neuroendocrine tumors: a single entity or a heterogeneous group? A retrospective analysis

PURPOSE

Grade 3 neuroendocrine tumor (NET G3) is a novel pathologic category within gastro-entero-pancreatic (GEP) neuroendocrine neoplasms (NENs) but its clinical behavior and therapeutic management still remain challenging. Prognostic and predictive factors aiding NET G3 management are needed.

PATIENTS AND METHODS

We performed a retrospective analysis from 2015 to 2020 of all patients with > 20% Ki-67, well-differentiated NETs evaluated within our NEN-dedicated multidisciplinary team. We divided the sample according the timing of NET G3 diagnosis, the radiotracers distribution and Ki-67. We analyzed the correlation between these NET G3 features and clinical outcomes.

RESULTS

Among 3238 multidisciplinary discussion reports, we selected 55 patients, 48 from GEP and 7 from an occult GEP origin. In 45 patients, NET G3 diagnosis occurred at the beginning of clinical history (upfront-NET G3), whereas in 10, during the NET G1-G2 clinical history (late-NET G3). Patients with ≤ 30% (34/55) vs. > 30% Ki-67 (21/55) had a better overall survival (OS) (p = 0.042); patients with a homogeneous vs. inhomogeneous/negative ⁶⁸Gallium(⁶⁸Ga)-DOTA-Peptide Positron Emission Tomography (PET)/computed tomography (CT) showed a trend to a better OS, and a significant better progression-free survival (PFS) (p = 0.033). A better OS was observed for negative/inhomogeneous vs. homogeneous 18-fluorodeoxyglucose (¹⁸FDG)-PET/CT (p = 0.027). A trend to a better OS was reported in late- vs. upfront-NET G3, while the latter showed a significantly better response rate (RR) (p = 0.048).

CONCLUSION

Our findings suggested that Ki-67 cutoff, functional imaging and the timing to NET G3 diagnosis may help clinicians in more accurate selection of NET G3 management. Prospective studies are needed.

Preliminary evaluation of alpha-emitting radioembolization in animal models of hepatocellular carcinoma

Hepatocellular carcinoma is the most common primary liver cancer and the fifth most frequently diagnosed cancer worldwide. Most patients with advanced disease are offered non-surgical palliative treatment options. This work explores the first alpha-particle emitting radioembolization for the treatment and monitoring of hepatic tumors. Furthermore, this works demonstrates the first in vivo simultaneous multiple-radionuclide SPECT-images of the complex decay chain of an [²²⁵Ac]Ac-labeled agent using a clinical SPECT system to monitor the temporal distribution. A DOTA chelator was modified with a lipophilic moiety and radiolabeled with the α-particle emitter Actinium-225. The resulting agent, [²²⁵Ac]Ac-DOTA-TDA, was emulsified in ethiodized oil and evaluated in vivo in mouse model and the VX2 rabbit technical model of liver cancer. SPECT imaging was performed to monitor distribution of the TAT agent and the free daughters. The [²²⁵Ac]Ac-DOTA-TDA emulsion was shown to retain within the HEP2G tumors and VX2 tumor, with minimal uptake within normal tissue. In the mouse model, significant improvements in overall survival were observed. SPECT-imaging was able to distinguish between the Actinium-225 agent (Francium-221) and the loss of the longer lived daughter, Bismuth-213. An α-particle emitting TARE agent is capable of targeting liver tumors with minimal accumulation in normal tissue, providing a potential therapeutic agent for the treatment of hepatocellular carcinoma as well as a variety of hepatic tumors. In addition, SPECT-imaging presented here supports the further development of imaging methodology and protocols that can be incorporated into the clinic to monitor Actinium-225-labeled agents.

Dosing Therapeutic Radiopharmaceuticals in Obese Patients

The prevalence of obesity has increased dramatically in the Western population. Obesity is known to influence not only the proportion of adipose tissue but also physiological processes that could alter drug pharmacokinetics. Yet, there are no specific dosing recommendations for radiopharmaceuticals in this patient population. This could potentially lead to underdosing and thus suboptimal treatment in obese patients, while it could also lead to drug toxicity due to high levels of radioactivity. In this review, relevant literature is summarized on radiopharmaceutical dosing and pharmacokinetic properties, and we aimed to translate these data into practical guidelines for dosing of radiopharmaceuticals in obese patients. For radium-223, dosing in obese patients is well established. Furthermore, for samarium-153-ethylenediaminetetramethylene (EDTMP), dose-escalation studies show that the maximum tolerated dose will probably not be reached in obese patients when dosing on MBq/kg. On the other hand, there is insufficient evidence to support dose recommendations in obese patients for rhenium-168-hydroxyethylidene diphosphonate (HEDP), sodium iodide-131, iodide 131-metaiodobenzylguanidine (MIBG), lutetium-177-dotatate, and lutetium-177-prostate-specific membrane antigen (PSMA). From a pharmacokinetic perspective, fixed dosing may be appropriate for these drugs. More research into obese patient populations is needed, especially in the light of increasing prevalence of obesity worldwide.

Synthesis and biological evaluation of novel PET tracers [18F]AG120 & [18F]AG135 for imaging mutant isocitrate dehydrogenase 1 expression

Mutations in isocitrate dehydrogenase 1 (IDH1) are commonly found in various human malignancies. Inhibitors of several mutant IDH1 enzymes have entered clinical trials as target therapeutic drugs for the treatment of patients with IDH1 mutations. Herein, we report the synthesis and evaluation of two 18F-labeled tracers, [18F]AG120 and [18F]AG135 for imaging expression of mutated IDH1 in positron emission tomography (PET). [18F]AG120 and [18F]AG135 were synthesized in decay-corrected radiochemical yield of 1 % and 3 %, respectively, high molar activity (52-66 MBq/nmol and 216-339 MBq/nmol, respectively) and high radiochemical purity (>99%). Both tracers showed good in vitro stability, selective uptake into mutated IDH1-expressing cells and good pharmacokinetic profiles with low uptake in most organs/tissues. Furthermore, [18F]AG120 micro-PET/CT imaging displayed significantly greater uptake in IDH1-mutant than in wild-type tumors, Relatively, uptake of [18F]AG135 was observed neither in IDH1-mutant tumor xenografts nor in wild-type tumors. This study suggests that [18F]AG120 is a promising radiotracer for PET imaging of IDH1 mutation, However, further optimization and investigation are necessary for [18F]AG135 due to the limited uptake in mutated IDH1-expressing tumors.

How does the Selection of Laboratory Mice Affect the Results of Physiological Distribution of Radiopharmaceuticals?

BACKGROUND

The choice of mice strain can significantly influence the physiological distribution and may lead to an inadequate assessment of the radiopharmaceutical properties.

OBJECTIVE

This work aims to present how the legal requirements that apply to radiopharmaceuticals contained in the various guidelines determine the choice of the mouse strain for quality control and preclinical studies and affect the results of physiological distribution.

METHODS

Swiss and BALB/c mice were chosen as commonly used strains in experiments for research and quality control purposes. Radiopharmaceuticals, i.e., preparations containing one or more radioactive isotopes in their composition, are subject to the same legal regulations at every stage of the research, development and routine quality control as all other medicines. Therefore, in vivo experiments are to be carried out to confirm the pharmacological properties and safety. Moreover, if a radiopharmaceutical's chemical structure is unknown or complex and impossible to be determined by physicochemical methods, an analysis of physiological distribution in a rodent animal model needs to be performed.

RESULTS

In our studies, thirty-six mice (Swiss n=18, BALB/c n=18) were randomly divided into six groups and injected with the following radiopharmaceuticals: [99mTc]Tc-Colloid, [99mTc]Tc-DTPA and [99mTc]Tc-EHIDA. Measurement of physiological distribution was conducted following the requirements of European Pharmacopoeia (Ph. Eur.) monograph 0689, internal instructions and the United States Pharmacopeia (USP) monograph. Additionally, at preclinical studies, ten mice (Swiss n=5, BALB/c n=5) were injected with the new tracer [99mTc]Tc-PSMA-T4, and its physiological distribution has been compared. The p-value <0.05 proved the statistical significance of the radiopharmaceutical physiological distribution.

CONCLUSION

We claim that mice strain choice can significantly influence the physiological distribution and may lead to inaccurate quality control results and incomprehensible interpretation of the results from preclinical in vivo studies of a new radiopharmaceutical.

Prognostic role of 11C-choline PET/CT scan in patients with metastatic castrate resistant prostate cancer undergoing primary docetaxel chemotherapy

BACKGROUND

We sought to assess the prognostic utility of 11C-choline positron emission tomography/computed tomography (PET/CT) in patients with metastatic castrate resistant prostate cancer (mCRPC) undergoing primary docetaxel chemotherapy.

METHODS

We performed a single institution retrospective analysis of 77 mCRPC patients who were treated with 6 cycles of docetaxel chemotherapy, and who also underwent 11C-choline PET/CT scans at baseline (before chemotherapy), mid-course (after 3 cycles), and posttherapy (after 6 cycles). We evaluated treatment response based on percent change in blood pool-corrected maximum standardized uptake value (SUVmax) of the target lesion on PET/CT, as well as percent change in serum prostate specific antigen (PSA). Logistic regression analysis was used to identify factors associated with complete treatment response. Progression free survival (PFS) analysis was performed using log-rank test and shown on Kaplan-Meier plot.

RESULTS

Percent change in blood pool-corrected SUVmax on mid-course scan was a significant predictor of complete response (odds ratio [OR]: 0.98, 95% confidence interval [CI]: 0.96-0.99, p = .0003), whereas percent change in PSA was not (OR: 0.99, 95% CI: 0.99-1.01, p = .6025). 57 of 77 patients (74%) achieved ≥20% reduction in blood pool-corrected SUVmax on mid-course; these patients were 3.6 times more likely to achieve complete response after full 6 cycles of docetaxel chemotherapy, compared to patients with <20% reduction in blood pool-corrected SUVmax (OR: 3.56, 95% CI: 1.04-16.52, p = .0420). Median PFS in the complete response group was 35.1 months (95% CI: 26.0-52.7 months), compared to 9.4 months (95% CI: 6.9-13.0 months) in the incomplete response group (p = .0005).

CONCLUSIONS

Our study showed that mid-course and posttherapy 11C-choline PET/CT evaluation for mCRPC patients undergoing primary docetaxel chemotherapy can predict full course treatment response and PFS, respectively. 11C-choline PET/CT imaging may provide valuable prognostic information to guide treatment choices for patients with mCRPC.

Relationship of In Vitro Toxicity of Technetium-99m to Subcellular Localisation and Absorbed Dose

Auger electron-emitters increasingly attract attention as potential radionuclides for molecular radionuclide therapy in oncology. The radionuclide technetium-99m is widely used for imaging; however, its potential as a therapeutic radionuclide has not yet been fully assessed. We used MDA-MB-231 breast cancer cells engineered to express the human sodium iodide symporter-green fluorescent protein fusion reporter (hNIS-GFP; MDA-MB-231.hNIS-GFP) as a model for controlled cellular radionuclide uptake. Uptake, efflux, and subcellular location of the NIS radiotracer [99mTc]TcO4- were characterised to calculate the nuclear-absorbed dose using Medical Internal Radiation Dose formalism. Radiotoxicity was determined using clonogenic and γ-H2AX assays. The daughter radionuclide technetium-99 or external beam irradiation therapy (EBRT) served as controls. [99mTc]TcO4- in vivo biodistribution in MDA-MB-231.hNIS-GFP tumour-bearing mice was determined by imaging and complemented by ex vivo tissue radioactivity analysis. [99mTc]TcO4- resulted in substantial DNA damage and reduction in the survival fraction (SF) following 24 h incubation in hNIS-expressing cells only. We found that 24,430 decays/cell (30 mBq/cell) were required to achieve SF0.37 (95%-confidence interval = [SF0.31; SF0.43]). Different approaches for determining the subcellular localisation of [99mTc]TcO4- led to SF0.37 nuclear-absorbed doses ranging from 0.33 to 11.7 Gy. In comparison, EBRT of MDA-MB-231.hNIS-GFP cells resulted in an SF0.37 of 2.59 Gy. In vivo retention of [99mTc]TcO4- after 24 h remained high at 28.0% ± 4.5% of the administered activity/gram tissue in MDA-MB-231.hNIS-GFP tumours. [99mTc]TcO4- caused DNA damage and reduced clonogenicity in this model, but only when the radioisotope was taken up into the cells. This data guides the safe use of technetium-99m during imaging and potential future therapeutic applications.

The role of histopathological and biochemical parameters for predicting metastatic disease on 68 Ga-PSMA-11 PET in prostate cancer

BACKGROUND

The aim of this study was to evaluate the role of histopathological and biochemical parameters in the prediction of the presence and number of PSMA positive lesions consistent with the metastatic spread of prostate cancer on ⁶⁸ Ga-PSMA PET images.

METHODS

Biochemical, histopathological and imaging data of 302 prostate cancer patients who underwent ⁶⁸ Ga-PSMA-11 PET/CT or PET/MR imaging for primary staging were retrospectively analyzed. Patients were divided into two groups as "PET positive" and "PET negative" according to the presence of pathologic extraprostatic PSMA involvement. "PET positive" patients were additionally divided into two groups: oligometastatic (1-3 metastatic lesion) and multimetastatic (>3 metastatic lesions).

RESULTS

The mean age of patients was 66.8 ± 7.6 years. Imaging modality was PET/MR in 223 (73.8%) and PET/CT in 79 (26.2%) of patients. Total PSA, PSA density (PSAD), ALP, and tumor ratio in biopsy specimens were found to be significantly higher in "PET positive" group compared to "PET negative" group and in multimetastatic group compared to oligometastatic group. PET positivity was observed in 3.8% of the low-intermediate risk groups (ISUP 1-3 and total PSA ≤ 20 ng/ml and PSAD < 0.15 ng/ml/cc). This ratio was 46% in the high-risk group (ISUP 4-5 or total PSA > 20 ng/ml or PSAD ≥ 0.15 ng/ml/cc) with a relative risk of 12 (p < .001). The prediction models to predict the PET positivity and the presence of distant metastasis had AUCs of 0.901 and 0.925, respectively; with ALP, total PSA, and tumor ratio in needle biopsy specimen as significant independent predictors (p < .05).

CONCLUSIONS

In this study, ⁶⁸ Ga-PSMA-11 PET positivity was significantly higher in the high-risk patient group than in the low-intermediate risk groups. The prediction models used for predicting the PET positivity and the presence of distant metastasis on PET imaging were successful with high discriminatory powers. In addition to total PSA and ISUP GG, ALP and tumor ratio in biopsy specimens can be used to identify high-risk patients.

Tau Biomarkers in Dementia: Positron Emission Tomography Radiopharmaceuticals in Tauopathy Assessment and Future Perspective

Abnormal accumulation of Tau protein is closely associated with neurodegeneration and cognitive impairment and it is a biomarker of neurodegeneration in the dementia field, especially in Alzheimer’s disease (AD); therefore, it is crucial to be able to assess the Tau deposits in vivo. Beyond the fluid biomarkers of tauopathy described in this review in relationship with the brain glucose metabolic patterns, this review aims to focus on tauopathy assessment by using Tau PET imaging. In recent years, several first-generation Tau PET tracers have been developed and applied in the dementia field. Common limitations of first-generation tracers include off-target binding and subcortical white-matter uptake; therefore, several institutions are working on developing second-generation Tau tracers. The increasing knowledge about the distribution of first- and second-generation Tau PET tracers in the brain may support physicians with Tau PET data interpretation, both in the research and in the clinical field, but an updated description of differences in distribution patterns among different Tau tracers, and in different clinical conditions, has not been reported yet. We provide an overview of first- and second-generation tracers used in ongoing clinical trials, also describing the differences and the properties of novel tracers, with a special focus on the distribution patterns of different Tau tracers. We also describe the distribution patterns of Tau tracers in AD, in atypical AD, and further neurodegenerative diseases in the dementia field.

Development of a triazolobenzodiazepine-based PET probe for subtype-selective vasopressin 1A receptor imaging

OBJECTIVES

To enable non-invasive real-time quantification of vasopressin 1A (V1A) receptors in peripheral organs, we sought to develop a suitable PET probe that would allow specific and selective V1A receptor imaging in vitro and in vivo.

METHODS

We synthesized a high-affinity and -selectivity ligand, designated compound 17. The target structure was labeled with carbon-11 and tested for its utility as a V1A-targeted PET tracer by cell uptake studies, autoradiography, in vivo PET imaging and ex vivo biodistribution experiments.

RESULTS

Compound 17 (PF-184563) and the respective precursor for radiolabeling were synthesized in an overall yield of 49% (over 7 steps) and 40% (over 8 steps), respectively. An inhibitory constant of 0.9 nM towards the V1A receptors was measured, while excellent selectivity over the related V1B, V2 and OT receptor (IC50 >10,000 nM) were obtained. Cell uptake studies revealed considerable V1A binding, which was significantly reduced in the presence of V1A antagonists. Conversely, there was no significant blockade in the presence of V1B and V2 antagonists. In vitro autoradiography and PET imaging studies in rodents indicated specific tracer binding mainly in the liver. Further, the pancreas, spleen and the heart exhibited specific binding of [11C]17 ([11C]PF-184563) by ex vivo biodistribution experiments.

CONCLUSION

We have developed the first V1A-targeted PET ligand that is suitable for subtype-selective receptor imaging in peripheral organs including the liver, heart, pancreas and spleen. Our findings suggest that [11C]PF-184563 can be a valuable tool to study the role of V1A receptors in liver diseases, as well as in cardiovascular pathologies.

Mucociliary Clearance Differs in Mild Asthma by Levels of Type 2 Inflammation

BACKGROUND

Although mucus plugging is a well-reported feature of asthma, whether asthma and type 2 inflammation affect mucociliary clearance (MCC) is unknown.

RESEARCH QUESTION

Does type 2 inflammation influence mucus clearance rates in patients with mild asthma who are not receiving corticosteroids?

STUDY DESIGN AND METHODS

The clearance rates of inhaled radiolabeled particles were compared between patients with mild asthma with low (n = 17) and high (n = 18) levels of T2 inflammation. Fraction exhaled nitric oxide (Feno) was used to prospectively segregate subjects into T2 Lo (Feno < 25 ppb) and T2 Hi (Feno > 35 ppb) cohorts. Bronchial brush samples were collected with fiber-optic bronchoscopy, and quantitative polymerase chain reaction was performed to measure expression of genes associated with T2 asthma. MCC rate comparisons were also made with a historical group of healthy control subjects (HCs, n = 12).

RESULTS

The T2 Lo cohort demonstrated increased MCC when compared with both T2 Hi and historic HCs. MCC within the T2 Hi group varied significantly, with some subjects having low or zero clearance. MCC decreased with increasing expression of several markers of T2 airway inflammation (CCL26, NOS2, and POSTN) and with Feno. MUC5AC and FOXJ1 expression was similar between the T2Lo and T2Hi cohorts.

INTERPRETATION

Increasing T2 inflammation was associated with decreasing MCC. High rates of MCC in T2 Lo subjects may indicate a compensatory mechanism present in mild disease but lost with high levels of inflammation. Future studies are required to better understand mechanisms and whether impairments in MCC in more severe asthma drive worse clinical outcomes.

David versus Goliath: Radiotheranostic nanomedicine as a weapon against melanoma

Malignant melanoma (MM), especially when diagnosed at an advanced stage, still represents a challenge for physicians. In recent years, immune check point inhibitors (ICI) have thoroughly changed MM landscape, although only 20-40% of MM patients respond to ICI. In MM progressing after ICI, treatment options, especially in case of MM not bearing V600 mutation, are limited. In this scenario, radionuclide theranostics, based on the sequential administration of a radiopharmaceuticals' pair, the first labeled with a radionuclide emitting energy suitable for imaging (i.e. positrons or gamma-rays), the second bound to another nuclide emitting particles for therapy, is particularly welcome. Melanocortin 1 Receptor (MC1R), strongly overexpressed by MM cells, has recently emerged as an interesting target for radionuclide theranostics. In the following, we briefly cover some emerging applications of MC1R-targeted radionuclide theranostics, also with reference to the potential of implementing some innovative nanotechnologies, such as gold nanoparticles, to move the field forward.

18F-FDG PET/CT imaging in the diagnosis of drug-induced lung disease and pulmonary infection in lymphoma

OBJECTIVE

Lymphoma is a hematological disease with high prevalence. Multi-cycle chemotherapy (CHT) or local radiotherapy is applied usually; however, adverse events have been reported, such as drug-induced lung disease (DILD). Positron emission tomography/computed tomography (PET/CT) is often used to evaluate the lesion, treatment effect, and prognosis of lymphoma. We investigated DILD and pulmonary infection (PI) after multi-cycle CHT in lymphoma patients, to identify DILD and PI, provide guidance for later treatment for them.

METHODS

In all, 677 patients diagnosed with lymphoma and who underwent CHT were included. These patients underwent 18fluorodeoxyglucose (18F-FDG) PET/CT before and after CHT at Shandong Cancer Hospital (affiliated with Shandong University) between April 2015 and November 2019. Fifty patients developed DILD, 41 patients had lung infections; lesion characteristics were analyzed based on clinical characteristics, laboratory examinations, and PET/CT imaging.

RESULTS

Among the 677 lymphoma patients, there were 50 cases of DILD, with an incidence rate of 7.4%. PET/CT showed an elevated 18fluorodeoxyglucose uptake lung background, septal thickening and reticulation, multiple ground glass-like shadows, and grid-shaped blur shadows, which were more common in the lung periphery and under the pleura. The maximum standardized uptake value in the lung was 2.45 ± 0.52. Pulmonary infections occurred in 41 patients, and the maximum standardized uptake value was 4.05 ± 1.42. Age, sex, CHT cycle, Ann-Arbor stage, and lymphocyte levels were not significantly different between DILD and PI patients. Leukocyte and neutrophils showed significant differences; the PI patients had increased laboratory indexes of leukocyte and neutrophils. The mean number of CHT cycles was 4 cycles for DILD and PI.

CONCLUSIONS

PET/CT imaging has high sensitivity and detection rates for primary and metastatic lymphoma lesions. DILD mostly occurs in the middle and late stages of CHT. Laboratory tests and PET/CT can evaluate the lesions and treatment effects, and provide guidance for subsequent treatment plans for patients.

Characterization of Intrinsically Radiolabeled Poly(lactic-co-glycolic acid) Nanoparticles for ex Vivo Autologous Cell Labeling and in Vivo Tracking

With the advent of novel immunotherapies, interest in ex vivo autologous cell labeling for in vivo cell tracking has revived. However, current clinically available labeling strategies have several drawbacks, such as release of radiolabel over time and cytotoxicity. Poly(lactic-co-glycolic acid) nanoparticles (PLGA NPs) are clinically used biodegradable carriers of contrast agents, with high loading capacity for multimodal imaging agents. Here we show the development of PLGA-based NPs for ex vivo cell labeling and in vivo cell tracking with SPECT. We used primary amine-modified PLGA polymers (PLGA-NH2) to construct NPs similar to unmodified PLGA NPs. PLGA-NH2 NPs were efficiently radiolabeled without chelator and retained the radionuclide for 2 weeks. Monocyte-derived dendritic cells labeled with [111In]In-PLGA-NH2 showed higher specific activity than those labeled with [111In]In-oxine, with no negative effect on cell viability. SPECT/CT imaging showed that radiolabeled THP-1 cells accumulated at the Staphylococcus aureus infection site in mice. In conclusion, PLGA-NH2 NPs are able to retain 111In, independent of chelator presence. Furthermore, [111In]In-PLGA-NH2 allows cell labeling with high specific activity and no loss of activity over prolonged time intervals. Finally, in vivo tracking of ex vivo labeled THP-1 cells was demonstrated in an infection model using SPECT/CT imaging.

Prediction of Long Bone Fractures in Multiple Myeloma Patients in an Advanced Imaging World

BACKGROUND

Multiple myeloma (MM) affects the long bones in 25% of patients. The advent of positron-emission tomography/computed tomography (PET/CT) scanners offers the possibility of both metabolic and radiographic information and may help determine fracture risk. To the best of our knowledge, no published study correlates these two factors with long bone fractures.

OBJECTIVES

To evaluate the impact of PET/CT on fracture risk assessment in multiple myeloma patients.

METHODS

We identified all bone marrow biopsy proven multiple myeloma patients from 1 January 2010 to 31 January 2015 at a single institution. We prospectively followed patients with long bone lesions using PET/CT scan images.

RESULTS

We identified 119 patients (59 males/60 females) with 256 long bone lesions. Mean age at diagnosis was 58 years. The majority of lesions were in the femur (n=150, 59%) and humerus (n=84, 33%); 13 lesions in 10 patients (8%) required surgery for impending (n=4) or actual fracture (n=9). Higher median SUVmax was measured for those with cortical involvement (8.05, range 0-50.8) vs. no involvement (5.0, range 2.1-18.1). SUVmax was found to be a predictor of cortical involvement (odds ratio = 1.17, P = 0.026). No significant correlation was found between SUVmax and pain or fracture (P = 0.43).

CONCLUSIONS

Improved medical treatment resulted improvement in 8% of patients with an actual or impending fracture. The orthopedic surgeons commonly use the Mirels classification for long bone fracture prediction. Adding PET/CT imaging to study in myeloma long bone lesions did not predict fracture risk directly but suggested it indirectly by cortical erosion.

Positron emission tomographic imaging in drug discovery

Positron emission tomography (PET) is an extensively used nuclear functional imaging technique, especially for central nervous system (CNS) and oncological disorders. Currently, drug development is a lengthy and costly pursuit. Imaging with PET radiotracers could be an effective way to hasten drug discovery and advancement, because it facilitates the monitoring of key facets, such as receptor occupancy quantification, drug biodistribution, pharmacokinetic (PK) analyses, validation of target engagement, treatment monitoring, and measurement of neurotransmitter concentrations. These parameters demand careful analyses for the robust appraisal of newly formulated drugs during preclinical and clinical trials. In this review, we discuss the usage of PET imaging in radiopharmaceutical development; drug development approaches with PET imaging; and PET developments in oncological and cardiac drug discovery.

Radiopharmaceutical and Eu3+ doped gadolinium oxide nanoparticles mediated triple-excited fluorescence imaging and image-guided surgery

Cerenkov luminescence imaging (CLI) is a novel optical imaging technique that has been applied in clinic using various radionuclides and radiopharmaceuticals. However, clinical application of CLI has been limited by weak optical signal and restricted tissue penetration depth. Various fluorescent probes have been combined with radiopharmaceuticals for improved imaging performances. However, as most of these probes only interact with Cerenkov luminescence (CL), the low photon fluence of CL greatly restricted it's interaction with fluorescent probes for in vivo imaging. Therefore, it is important to develop probes that can effectively convert energy beyond CL such as β and γ to the low energy optical signals. In this study, a Eu3+ doped gadolinium oxide (Gd2O3:Eu) was synthesized and combined with radiopharmaceuticals to achieve a red-shifted optical spectrum with less tissue scattering and enhanced optical signal intensity in this study. The interaction between Gd2O3:Eu and radiopharmaceutical were investigated using 18F-fluorodeoxyglucose (18F-FDG). The ex vivo optical signal intensity of the mixture of Gd2O3:Eu and 18F-FDG reached 369 times as high as that of CLI using 18F-FDG alone. To achieve improved biocompatibility, the Gd2O3:Eu nanoparticles were then modified with polyvinyl alcohol (PVA), and the resulted nanoprobe PVA modified Gd2O3:Eu (Gd2O3:Eu@PVA) was applied in intraoperative tumor imaging. Compared with 18F-FDG alone, intraoperative administration of Gd2O3:Eu@PVA and 18F-FDG combination achieved a much higher tumor-to-normal tissue ratio (TNR, 10.24 ± 2.24 vs. 1.87 ± 0.73, P = 0.0030). The use of Gd2O3:Eu@PVA and 18F-FDG also assisted intraoperative detection of tumors that were omitted by preoperative positron emission tomography (PET) imaging. Further experiment of image-guided surgery demonstrated feasibility of image-guided tumor resection using Gd2O3:Eu@PVA and 18F-FDG. In summary, Gd2O3:Eu can achieve significantly optimized imaging property when combined with 18F-FDG in intraoperative tumor imaging and image-guided tumor resection surgery. It is expected that the development of the Gd2O3:Eu nanoparticle will promote investigation and application of novel nanoparticles that can interact with radiopharmaceuticals for improved imaging properties. This work highlighted the impact of the nanoprobe that can be excited by radiopharmaceuticals emitting CL, β, and γ radiation for precisely imaging of tumor and intraoperatively guide tumor resection.

Green tea essential oil encapsulated chitosan nanoparticles-based radiopharmaceutical as a new trend for solid tumor theranosis

The existing study is embarked on investigating the antineoplastic activity of green tea essential oil (GTO) as a natural product. In this regard, GTO was encapsulated in cationic chitosan, nitrogenous-polysaccharide derived by partial deacetylation of chitin, nanoparticles (CS NPs) with entrapment efficiency (EE%) of 81.4 ± 5.7% and a mean particle-size of 30.7 ± 1.13 nm. Moreover, the cytotoxic effect of CS/GTO NPs was evaluated versus human liver (HepG-2), breast (MCF-7) and colon (HCT-116) cancer cell-lines and exhibited a positive impact when compared to bare CS NPs by 3, 2.3 and 1.7 fold for the three cell lines, respectively. More interestingly, CS/GTO NPs were complexed with technethium-99m (^99mTc) radionuclide. With a view to achieve a successful radiolabeling process, different parameters were optimized resulting in a radiolabeling efficiency (RE%) of 93.4 ± 1.2%. Radiopharmacokinetics of the radiolabeled NPs in healthy mice demonstrated a reticuloendothelial system (RES) evading and long blood circulation time up to 4 h. On the other hand, the biodistribution profile in solid tumor models showed 20.3 ± 2.1% localization and cancer cell targeting within just 30 min. On the whole, the reported results encourage the potential use of CS/GTO NPs as a side effect-free anticancer agent and its ^99mTc-analogue as a novel CS/GTO NPs-based diagnostic-radiopharmaceutical for cancer.

Preclinical Testing of Radiopharmaceuticals for the Detection and Characterization of Osteomyelitis: Experiences from a Porcine Model

The development of new and better radioactive tracers capable of detecting and characterizing osteomyelitis is an ongoing process, mainly because available tracers lack selectivity towards osteomyelitis. An integrated part of developing new tracers is the performance of in vivo tests using appropriate animal models. The available animal models for osteomyelitis are also far from ideal. Therefore, developing improved animal osteomyelitis models is as important as developing new radioactive tracers. We recently published a review on radioactive tracers. In this review, we only present and discuss osteomyelitis models. Three ethical aspects (3R) are essential when exposing experimental animals to infections. Thus, we should perform experiments in vitro rather than in vivo (Replacement), use as few animals as possible (Reduction), and impose as little pain on the animal as possible (Refinement). The gain for humans should by far exceed the disadvantages for the individual experimental animal. To this end, the translational value of animal experiments is crucial. We therefore need a robust and well-characterized animal model to evaluate new osteomyelitis tracers to be sure that unpredicted variation in the animal model does not lead to a misinterpretation of the tracer behavior. In this review, we focus on how the development of radioactive tracers relies heavily on the selection of a reliable animal model, and we base the discussions on our own experience with a porcine model.